Paper machines have suction rolls of various types at the wire part and press part thereof for dehydration or squeezing. Typical suction rolls include a suction couch roll, a suction pickup roll, a suction press roll, and a linger roll. These rolls comprise a revolving shell with a number of openings which is made of stainless steel or bronze and a fixed suction box inside the shell by which liquid is sucked up. However, with the progress of paper making, insoluble matters of various inorganic components, loading materials, fibers, resinous components, etc., contained in white water stick to the shell to form scales. The formed scales plug the shell openings to gradually reduce a dehydrating, squeezing or sucking function, not only resulting in deterioration of the operation rate or operational efficiency but causing unevenness in the water content of paper which would lead to deteriorated quality, such as poor formation and uneven drying properties. Besides, the portion of the roll in direct contact with the scales is susceptible to corrosion, ultimately leading to breaking of the roll in the worst situation.
In paper manufacturing factories, this problem has been coped with by periodically exchanging suction rolls. Since the rate of plugging is frequently accelerated through variation of operating conditions, the paper machine must sometimes be suspended for exchange of rolls on shorter schedules.
The scales plugging the suction roll after an exchange are usually removed by mechanical outer force with a drill or an ultra-high-pressure water jet, thereby making the roll reusable. However, since the scales are very hard and rigid and also the shell has a vast number of openings of from tens of thousands to hundreds of thousands, such mechanical treatment not only entails much labor but is liable to damage the shell openings or areas surrounding the same.
Therefore, it has been keenly demanded in the field of paper manufacturing to develop an effective method for continuously preventing suction rolls from plugging, but no method serving the purpose has been reached.